In the Ethernet technology, a MAC (Medium Access Control, Medium Access Control) layer is located at a data link layer; and sublayers such as PCS (Physical Coding Sublayer, physical coding sublayer), FEC (Forward Error Correction, forward error correction), PMA (Physical Medium Attachment, physical medium attachment), and PMD (Physical Medium Dependent, physical medium dependent) are located at a physical layer. Interconnection between the data link layer and the physical layer is implemented by an MII (Media Independent Interface, media independent interface) electrical interface. One Mac address identifies one Ethernet port, and one MAC port is connected to one physical layer interface by using a corresponding MII.
To meet an increasing demand on a network data traffic speed, a rate of a MAC port continuously increases. The rate of a MAC port rate increases by tenfold. For example, the rate of a MAC port (the rate of a MAC port is determined by bandwidth of a physical layer interface) continuously evolves from 10 Mbps to 100 Mbps, 1 Gbps, 10 Gbps, and 100 Gbps, and from 40 Gbps to 400 Gbps. One MAC port is connected only to one physical layer interface, and the rate of a MAC port generally increases by tenfold, but bandwidth required in actual application does not necessarily increase by tenfold; therefore, a transmission apparatus in the prior art has relatively great limitations. For example, efficient support for an Ethernet MAC port with a rate of 50 Gbps, 60 Gbps, 150 Gbps, and so on is insufficient, which further causes low utilization of interface bandwidth when there is a relatively great difference between bandwidth required in actual application and bandwidth of a physical layer interface. For example, if a 100GE physical interface module is used to support a MAC port with a rate of 50 Gbp, 50% of capacity of the 100GE physical interface module is wasted.